The invention relates to a thread brake generally of the kind having two co-axial braking surface rings arranged in spaced relationship to one another, and a capsule shaped braking cartridge whose rounded (hemispherical) ends bear against the braking surface rings.
Thread brakes of this general kind are disclosed in Germah Patent Specification No. 15 10 807 for example.
For a thread to be threaded through the brake, and in particular, for it to be so threaded pneumatically, it is necessary to provide an unobstructed passage for the thread, this being done by disengaging the braking cartridge from the two braking surface rings, as a result of which two passages through the braking surface rings are opened. In a thread brake of the kind described above which is disclosed in German Offenlegungsschrift No. 23 09 578, which brake is used in conjunction with a two-for-one twisting spindle having an entry tube for a thread, the lower braking surface ring is moved downwards by forcing down the thread entry tube, as a result of which the capsule shaped braking cartridge, which consists at least in part of a ferromagnetic material, is drawn sideways and held by a permanent magnet situated in the region of the outer surface of the brake housing. In this way at least part of the threading passage is cleared to enable the thread to be threaded mechanically or pneumatically through the braking chamber, that is to say, through the brake housing.
In a thread brake described in German Auslegeschrift No. 25 43 018, which is likewise associated with a two-for-one twisting spindle and which has a capsule shaped braking cartridge, the cartridge is compressed downwards by forcing down the thread entry tube and the upper braking surface fastened to the said entry tube of the two-for-one twisting spindle, and the cartridge is then moved sideways by a tubular bridging piece in such a way that the said tubular bridging piece moves to a central threading position.
In the known thread brakes in which the braking cartridge moves away from the central position and is then held in a laterally displaced position, it may happen that the cartridge, when it returns to its central braking position, tilts or goes askew, which may adversely affect the movement of the thread which has now been threaded through. The main reason why there is this danger of the cartridge tilting or skewing, even if only momentarily, is that when the cartridge is released by holding magnets, which may for example be laterally situated, the release of the cartridge is not entirely uniform. Apart from this, the fact that displacing members to move the cartridge temporarily away from the central position also have to be provided is a disadvantage both from the point of view of the additional design costs and also from the operators point of view when operating the apparatus, because, in the course of pneumatic threading for example, additional operations have to be performed to force down the thread entry tube.
GB Patent Specification No. 1 505 744 discloses a thread brake for a two-for-one twisting spindle in which the passage for the thread to pass through the brake housing is widened out locally into a pocket, of which the inclined upper end face is in the form of a flat fixed braking surface which is inclined to one side and extends in a circle around the opening of the thread passage through which the thread enters the pocket; and in which the braking member is in the form of a braking plate of ferromagnetic material which covers the opening through which the thread enters. The thread, as it passes through the brake, is capable of pivoting this plate back from the fixed braking surface, in the direction in which the thread moves, about a pivot point situated in the region of the top of the outer edge of the plate, in opposition to the force exerted by a multi-pole permanent magnet which can be adjusted relative to the fixed braking surface. To enable a thread to be threaded pneumatically through a thread brake of this kind, it is known to pivot the braking plate by moving the tube through which the thread passes or else to lift it away from the braking surface by means of thrust pins lying parallel and adjacent to the said tube. To enable externally operable mechanical displacing members of this kind to be dispensed with, it is also known from GB Patent Specification No. 1 505 744 to provide a by-pass passage in the fixed braking surface so as to connect with the passage for the thread, through which by-pass passage the thread is passed during the pneumatic threading process without the braking plate being lifted clear of the braking surface. When tension is applied to the thread which has been through the brake, the thread becomes tight and is drawn out of the by-pass passage into the actual, i.e. effective, braking area.
In comparison with so-called plate-type thread brakes of this kind, so-called capsule-type thread brakes with a capsule-shaped braking cartridge have the advantage that there are at least two braking points, namely one in the region of the upper braking surface ring and another in the region of the lower braking surface ring, the thread moving continuously to and fro along the braking surface rings, and as it does so at the same time rubbing over the rounded or hemispherical ends of the braking cartridge. This means that the braking surfaces are kept clean at all times, thus ensuring that the thread brake remains fully operational for long periods.